This invention relates to printers for printing data on a print medium, and more particularly to an improvement in the printer and its method of operation by which the ink ribbon is advanced in a way which will avoid problems due to ink depletion in the ribbon.
Ribbon ink depletion is recognized as a problem for printers capable of printing dense patterns or graphics. The ribbon is typically moved at a slower rate of speed than the print head carrier, and ink depletion occurs when successive dense patterns on a line overprint a section of the ribbon. This overprinting causes the images of later patterns to be printed lighter, and this is undesirable, particularly when printing color-filled images.
A number of approaches have been taken in addressing this problem. The most popular solution has employed a motor to continually drive the ribbon, and has been adopted in many small and intermediate printers. However, the use of a separate ribbon feed motor adds significantly to the cost of the printer, and may result in a higher than desirable rate of ribbon consumption.
In many printers, particularly the smaller, lower cost printers, the ink ribbon is advanced by a mechanical linkage between the ribbon drive and the print head carrier motor so that movement of the print head by the carrier motor will also advance the ribbon. Differential ribbon ink depletion is especially troublesome in this type of printer.
An object of the present invention is to provide a method and means for intelligently advancing the ribbon in a printer to avoid ribbon ink depletion, and which is suitable for use in a printer of the above-described type wherein movement of the print head controls the advancement of the ink ribbon.